We use the Frio when the pouch doesn't have to be waterproof. For waterproofing, we use either a Pelican box or an Aquapac waterproof bag. Pelican boxes are great for on a boat, wearing a PFD (mine tucks in nicely on the side straps), or someplace where the bulk isn't an issue. The Aquapac bags are great for when the EpiPens will be under water a lot (i.e. swimming) and that will keep it cool. I've worn it under a PFD as well. You can get Aquapac bags that are big enough to fit over the Frio but then the Frio cannot breathe and stay as cool as possible... so it's not perfect.
Yes, $27 for one large Frio pouch is normal. The Large will fit two Epis comfortably. They are imported from the UK and well made. Worth the money!